"µ" is Greek for "M" so it should be Micro DAC, not U-DAC. Sorry about that.
I'm using it in Class A right now with the Beats by Dr. Dre Solo HD. Holly cow! this thing sounds GREAT!
Edited by HiFiGuy528 - 5/18/13 at 8:13am
No it doesn't auto switch, so yes you have to turn off the speakers when you want to listen to headphones only. I did notice that it lessens the volume of the RCA out when you plug in headphones. I've encountered this while using USB power. :)
The only issue I have with the uDAC-HD is there is no way to control the volume except with the player or with your device. I'm using Foobar and when using the uDac-HD (using power supply) to drive my headphones (Senn HD558), it's a bit too loud to increase the Foobar volume past 50%. Do you experience this as well?
Also, I'm thinking of upgrading my headphones to the HD 650, I noticed you have them. Care to share some impressions using this with the uDAC-HD?
I don't use those apps so I don't have any suggestions. On a Mac it's easy to move the volume by 1/4 steps with Option+Shift.
The HD650 is a bit on the warm/rich sounding side for me, but on the uDAC it is more tolerable. This little guy has a ton of resolution. With the power supply, the headphones amp is really good. BTW, I use a 9v DC battery pack to take the DAC off the power grid.